1. Field of the Invention
The present invention relates to circulatory devices in large buildings and, in particular, concerns a cooling fan having reinforced blades that may be used to circulate a large volume of air.
2. Description of the Related Art
People who work in large buildings, such as warehouses and airport hangers, are routinely exposed to working conditions that range from being uncomfortable to hazardous. On a hot day, the inside air temperature may reach a point where a person is unable to maintain a healthy body temperature. Moreover, many activities that occur in these environments, such as welding or operating internal combustion engines, create airborne contaminants that may be deleterious to those exposed. The effects of airborne contaminants are magnified to an even greater extent if the area is not properly vented.
The problem of cooling or circulating air in large buildings may not be solved by conventional air conditioning methods. The large volume of air within the building in conjunction with the large rate of heat conducted through ceilings and walls may require powerful air conditioning devices to be effective. If such devices were used, the operating costs would be substantial. Also, conventional air conditioning routinely re-circulates the internal air for added cooling efficiency. Therefore, conventional air conditioning is not typically used in ventilation systems that serve to rapidly remove airborne contaminants, such as exhaust or smoke, and replace the contaminated air with fresh air from an outside source. For example, when welding and operating internal combustion engines within a structure, the internal air must be replaced and should not be re-circulated due to an unhealthy accumulation of airborne contaminants.
In general, small and large diameter fans may be used to provide some degree of circulation, cooling, and ventilation when conventional air conditioning is not feasible. A drawback of using small diameter fans to circulate air is that the resulting airflow dramatically tapers-off at downstream locations. Also, the large amount of electrical power required by the simultaneous use of these devices in great numbers negates their advantage as an inexpensive cooling system.
Moreover, a drawback to using large diameter fans is that they typically require specially constructed high-strength light-weight blades that may withstand large stresses caused by significant gravitational torques that increase with an increasing blade length to width aspect ratio. The fact that the rotational inertia of the fan increases with the square of the diameter requires the use of high torque producing gear reduction mechanisms. Unfortunately, conventional drivetrain components may be susceptible to mechanical failure due to the substantially large torque produced by electric motors during their startup phase, which may decrease the reliability of large diameter fans.
Certain large diameter fans have been equipped with low speed mechanisms and large fan blades with aerodynamic features. For instance, U.S. Pat. No. 6,244,821 discloses a low speed cooling fan having a large diameter with proportionally large fan blades that may be formed using a generally known extrusion process. Unfortunately, such extruded blades have unsupported trailing edges that may tear from deforming or warping during formation and cooling. As a result, the aerodynamic features are shortened due to tearing created on longer unsupported trailing edges during fabrication, which reduces the overall performance of the large fan blades. Therefore, the shortened trailing edges adversely impact the aerodynamic effectiveness of the large fan blades thereby potentially diminishing the efficiency of generated circulatory air flow within a structure.
From the foregoing, there currently exists a need for a cost efficient circulatory device that provides optimal ventilation and effective cooling in large buildings. In particular, there currently exists a need for such a circulatory device that comprises improved fan blades and a method of manufacturing the same so as to increase the structural rigidity of the blade and maintain the enhanced aerodynamic performance.